1. Field of the Invention
The present invention relates to a sheet-shaped medium treatment apparatus capable of effectively carrying out sheet-shaped medium treatments such as collating sheet-shaped mediums, sorting the sheet-shaped mediums, forming image thereon, after-treating the sheet-shaped mediums and the like.
2. Description of the Prior Art
As a means for carrying out collating in a piling state on a tray of piling means and sorting sheet-shaped mediums on which image is formed and which are conveyed successively at a constant interval, a unknown sheet-shaped medium treatment apparatus has been suggested.
As shown in FIG. 44 and FIG. 45, this sheet-shaped medium treatment apparatus generally comprises a discharging means having a paper-discharging roller 3 consisting of a pair of lower roller 3a and upper roller 3b for discharging the sheet-shaped mediums to be conveyed, a piling means (hereinafter, referred to as a tray 12) for piling the sheet-shaped mediums discharged from the discharging means, an arranging means (not shown in FIG. 44 and FIG. 45 and described later) for arranging the sheet-shaped mediums piled on the tray 12 by contacting with end portions parallel to their discharge direction a from the discharging means, so as to sandwich them, a sorting means (tray shifting means or arranging member driving means) for sorting the sheet-shaped mediums by shifting the tray 12 or the arranging means by a predetermined amount in a shift direction d perpendicular to the discharge direction a and a return means comprised of a rotational body capable of contacting with and separating from the sheet-shaped mediums for carrying out return operations of moving the sheet-shaped mediums by means of rotation in contact with the sheet-shaped mediums to bring them into contact with a vertical wall (hereinafter, referred to as an end fence), which is provided at the upstream end of the tray 12 in the discharge direction a, to thereby collate the sheet-shaped mediums,
In FIG. 44 and FIG. 45, return rollers 121a and 121b constructing the part of the return means are shown.
This sheet-shaped medium treatment apparatus is constructed as a part of an image forming apparatus or to include a sheet-shaped medium after-treatment apparatus, for carrying out a longitudinal arrangement of collating the sheet-shaped mediums to be conveyed successively in the discharge direction and a transverse arrangement of collating the sheet-shaped mediums in a direction perpendicular to the discharge direction and, if necessary, for carrying out a sorting process.
For collating the sheet-shaped mediums, arranging operation by the arranging means or return operation by the return means is carried out and for sorting the sheet-shaped mediums, sorting operation by the sorting means is carried out. In this case, each operation for collating or sorting the sheet-shaped mediums is carried out by a constant time interval at which the sheet-shaped mediums are conveyed successively.
For example, In a period after a sheet-shaped medium is discharged onto the tray before a next sheet is discharged, (1) return operation for arranging the sheet-shaped medium in the discharge direction by returning the sheet-shaped medium till coming into contact with the end fence by means of the return means, in order to arrange the sheet-shaped medium right after discharging in the same line as end edges of the discharging-completed sheet-shaped mediums in the discharge direction, (2) arranging operation for sandwiching ends of the sheet-shaped mediums together with the discharging-completed sheet-shaped mediums in the shift direction d by use of the arranging means, in order to arrange end edges of the sheet-shaped mediums in the shift direction d and (3) after the last sheet-shaped mediums of a part are discharged and before the first sheet-shaped medium of next part is discharged, sorting operation for shifting the tray 12 (or shifting the arranging members) by a predetermined amount, are carried out.
In such unknown paper after-treatment apparatus, when the sheet-shaped mediums received from the image forming apparatus are conveyed and are discharged and piled on the tray 12 sheet by sheet via a paper-discharging roller 3, the sheet-shaped mediums were collated and piled much depending on the self-weight dropping of the sheet-shaped mediums. That is, the tray 12 is mounted such that a side close to the discharging outlet (downstream side in the discharge direction a) becomes lower than a side distant from the discharging outlet (upstream side in the discharge direction a), by a constant angle, for example, an angle α.
By this, the sheet-shaped mediums dropped on the tray 12 slide toward the upstream side in the discharge direction along the slope. In sliding, the sheet-shaped mediums get in contact with return rollers 121a and 121b that are fired under the paper-discharging roller 3 to contact with and separate from the piled papers, and rear ends of the sheet-shaped mediums get in contact with the end fence 131 to be arranged by means of rotating force of these return rollers.
The rear ends of sheet-shaped mediums discharged from the discharging roller 3 are picked out from the discharging roller 3 and then the sheet-shaped mediums are dropped on the tray 12 along the outer circumference surface of the return rollers 121a and 121b placed under the discharging roller 3. However, right after the drop, the rear ends of the sheet-shaped mediums are not in contact with the return rollers 121a and 121b and when the sheet-shaped mediums slide toward the end fence along slope of the tray 12, the rear ends first get in contact. If the sheet-shaped mediums get in contact with the return rollers, they are drawn by means of the rotating force of return rollers 121a and 121b. 
However, for example when the sheet-shaped mediums having back curls (downward curls) with middle height are piled in large quantities on the tray 12, slope angle of the piling surface becomes gentle to θ smaller than α and it is more difficult for the sheet-shaped mediums dropped on the tray to return, because of slope of the piling surface. If the sheet-shaped mediums do not return, they can not be in contact with the return rollers 121a and 121b, so that the sheet-shaped mediums might not return till they get in contact with the end fence 131 not to be uniform.
Also, regardless of curling direction, as shown in FIG. 45, when paper S1 as the sheet-shaped medium is discharged, the rear end thereof may not be caught by the return rollers 121a and 121b. So, when the front end of the discharged paper S1 gets in contact with papers S2 already piled on the tray 12, the piled paper S2 is extruded in the discharge direction a by the discharged paper S1 and as a result, not-uniformity takes place as shown in FIG. 45.